NUCLEAR FUEL ASSEMBLY

1,256,198. Fuel elements. GENERAL ELECTRIC CO. 14 Aug., 1970 [15 Aug., 1969], No.39415/70. Heading G6C. A nuclear fuel assembly comprises a plurality of fuel rods in spaced array between upper and lower tie plates, a removable open-ended tubular flow channel surrounding the array and adapted to fit adjacent a peripheral surface of one of the tie plates, and restraining means attached to this tie plate for restraining lateral movement of the flow channel away from the tie plate. As shown in Fig. 3a, flow channel 36 is a sliding fit over a lower tie plate 27 formed with a nose piece 17 having openings 39 to receive pressurized coolant which flows upward among the fuel rods 26. To avoid stagnation of the coolant in the spaces between fuel assemblies mounted in a reactor core, a portion (of the order of 5 to 6%) of the coolant is allowed to leak into these spaces from between the tie plate 27 and the flow channel 36. (Coolant may also leak through passages 48 in the tie plate 27 and/or through passages 49 in the flow channel 36). Leakage is controlled by limiting the deflection of the flow channel 36 away from the tie plate 27, by means of a sleeve 40 which abuts an inner shoulder 41 formed on the tie plate and is welded, as at 42, to an outer shoulder 43. The sleeve 40 and the peripheral surface 44 of the tie plate 27 thus form a longitudinally opening slot for receiving the lower portion of the flow channel 36. The leakage flow path is thus substantially lengthened, increasing the leakage flow resistance, and the sleeve 40 substantially prevents the deflection of the flow channel 36 away from the tie plate 27. In a modified version the sleeve 40 is formed with corrugations to increase the leakage flow resistance and increase the rigidity of the sleeve. In a second embodiment (Fig. 4, not shown) the lower tie plate is fitted with a series of headed studs for engaging a corresponding series of longitudinal open-ended slots in the lower end of the flow channel. In a third embodiment (Fig. 5, not shown) a longitudinally opening groove or seat formed in the lower tie plate receives the lower end of the flow channel. Since the groove or seat is relatively shallow, a retainer spring arrangement is provided for urging the flow channel into engagement with the channel retainer seat.